Non-magnetic iron-nickel-chromium-molybdenum alloy,and watch springs obtained with this alloy



United States Patent 3,464,815 NON-MAGNETIC IRON-NICKEL-CHROMIUM-MOLYBDENUM ALLOY, AND WATCH SPRINGS OBTAINED WITH THIS ALLOY XavierWache, Sauvigny-les-Bois, Nievre, France, assignor t0 SocitMetallurgique dlmphy, Paris, France, a

French company No Drawing. Filed June 22, 1967, Ser. No. 647,956

Claims priority, application France, July 12, 1966, Int. Cl. C22c 39/20,39/50 U.S. Cl. 75-124 3 Claims ABSTRACT OF THE DISCLOSURE Watch springsare characterized by four parameters well known to those who specialisein watch-making, namely the heat coefficient, isochronism factor,position distances and secondary error.

The heat coefiicient is a basic parameter characterizing the sensitivityof the spring to variations in ambient temperature. The other threeparameters will not be described here, since they are not directlyconcerned with the invention.

The heat coeflicient is dependent on the thermoelastic coefficient ofthe alloys used for the manufacture of the spring. The thermoelasticcoefficient indicates the effect of temperature variations on themodulus of elasticity of the alloys.

One of the aims in the manufacture of a watch spring is to obtain a zeroheat coeflicient. This can be done by using an alloy having a zerothermoelastic coefficient under the operating conditions of the spring.

One of the solutions of this problem already proposed by the applicantsis to make these springs of a type of alloy known as Elinvar, which is atrademark filed in the name of Socit Metallurgique d'Imphy.

The nominal composition of an alloy of this kind is as follows:

Percent C 0.7 Si 0.3 Mn 1.9 Ni 32 Cr 10 W 3.5 Fe Remainder Percent CMinimum Si Minimum Mn Minimum Ni 42 Percent Ti 2.5 A1 1 Fe RemainderDurinval alloys are distinguished from Elinvar alloys in particular bytheir hardening mechanism. The mechanical characteristics of Elinvar areproduced by appropriate heat treatment during which chromium carbidesare precipitated, while titanium nickelides and aluminium nickelides areprecipitated in the case of Durinval. This essential diiference in thehardening mechanisms of the two types of alloy is, of course, directlyconnected with differences in composition, which a comparison of theabove two analyses will reveal. Quite apart from their higher elasticlimit, Durinval alloys, like Elinvar alloys, have, of course, asubstantially zero thermoelastic coefficient in the region of ambienttemperature.

But they cannot be used to make watch springs whose movement is notmechanical but electrical. For watch springs with electrical movementsmust be non-magnetic at ambient temperature, whereas Durinval alloys arehighly magnetic under these conditions. Their Curie point, i.e. thetemperature at which the alloy passes from the ferromagnetic to theparamagnetic state, is about This invention relates to a new group ofalloys that have the usual features of conventional Durinval alloys, butare non-magnetic at ambient temperature.

The applicants have found that the Curie point of Durinval alloys can begreatly reduced by appropriate additions of molybdenum, while all thedesired features, and in particular a zero thermoelastic coeflicient,are preserved in the resulting material by adjusting the contents of theother elements.

The invention relates to a non-magnetic alloy characterized in that itis composed of the following, by weight: 36.5 to 39.5% of nickel, 1.5 to4.5% of chromium, 1.5 to 3% of molybdenum, 0.75 to 1.25% of aluminiumand 2.3% of titanium, together with very small quantities of carbon,silicon, manganese, sulphur and phosphorus, the remainder being iron.

The invention also relates to watch springs made of this alloy.

The following composition by weight of an alloy according to theinvention may be given as an example: carbon 0.005%, silicon 0.34%,manganese 0.16%, nickel 38.4%, chromium 3.37%, molybdenum 2%, titanium2.46%, aluminium 0.96% and iron 52.29%, the remainder being sulphur andphosphorus. The Curie point of this alloy is below 18 and it ispractically non-magnetic at ambient temperature, having a zerothermoelastic coefficient.

The research on which the invention is based has shown that the contentsof the constituent elements of the alloy must be adjusted within thefollowing limits to obtain a set of properties similar to those of thealloy mentioned above by way of example:

Percent Nickel 36.5-39.5 Chromium 1.5-4.5 Molybdenum 1.5-3 Aluminium0.75-1.25 Titanium 2-3 The remainder is iron, carbon, silicon,manganese, sulphur and phosphorus in very small proportions.

To obtain the best results within the composition ranges indicatedabove, account must be taken of the sometimes contradictory effects onthe Curie point of variations in the contents of the various elements.Within the composition range in question, additions of nickel raise theCurie point, while additions of chromium, molybdenum, titanium andaluminium lower it.

Account must also be taken of the efiect on the Curie point of themanner in which the alloy hardens during its treatment. Theprecipitation of titanium nickelides and aluminium nickelides makes thematrix of the alloy relatively poor in nickel, and is thereforeaccompanied by a lowering of the Curie point.

The invention is not, of course, limited by the details of the processthat have just been described. These may be modified without goingbeyond the scope of the invention.

I claim 1. Non-magnetic iron-nickel-chromiummolybdenum alloy,characterized in that it is composed, by Weight, of 36.5 to 39.5% ofnickel, 1.5 to 4.5% of chromium, 1.5 to 3% of molybdenum, 0.75 to 1.25%of aluminium and 2 to 3% of titanium, the remainder being iron, together with very small quantities of carbon, silicon, manganese, sulphurand phosphorus.

2. A non-magnetic alloy as claimed in claim 1, characterized in that itis composed by Weight of 38.4% of nickel, 3.37% of chromium, 2% ofmolybdenum, 0.96%

of aluminium, 2.46% of titanium, 52.29% of iron, 0.005% of carbon, 0.34%of silicon and 0.16% of manganese, the remainder being sulphur andphosphorus.

3. Watch springs, characterized in that they are made of a non-magneticiron-nickel-chromii1m-molybdenum alloy, composed, by weight, of 36.5 to39.5% of nickel, 1.5 to 4.5% of chromium, 1.5 to 3% of molybdenum, 0.75to 1.25% of aluminium and 2 to 3% of titanium, the remainder being iron,together with very small quantities of carbon, silicon, manganese,sulphur and phosphorus.

References Cited UNITED STATES PATENTS 3,065,068 11/1962 Dyrkacz 75l28.83,243,287 3/1966 Lillys 75--128.8 3,300,347 1/1967 Kasza 75-124 HYLANDBIZOT, Primary Examiner US. Cl. X.-R. 75128

